Although the Minister for Transport has been privately critical about the "thoroughness" of the penalty points investigation conducted by Assistant Garda Commissioner John O'Mahony, as well as Mr Callinan's well-publicised comments about the garda whistleblowers, these are just two of several issues which have placed him on a collision course with justice authorities.

Mr Varadkar has also been increasingly frustrated with Mr Shatter, the gardai and the Courts Service over perceived obstacles and delays related to a number of road safety initiatives in recent months.

The main concern of Mr Varadkar, who lost a relative in a road traffic accident, is that he does not believe his reform agenda is being embraced sufficiently.

While this tragedy is not the main motivation behind his efforts to make our roads safer, Mr Varadkar has referenced it on a number of occasions and believes it has helped his understanding of the issues involved.

A source told the Sunday Independent: "Leo is incredibly committed to improving road safety and minimising the number of traffic deaths. But he has been quite frustrated by the obstacles placed in his path."

Key issues of concern for him include:

* The non-enforcement of legislation requiring motorists charged with road traffic offences to produce a copy of their driving licence in court, which has allowed offenders avoid having points attached to their licence.

* The continued use of the poor box by some judges, allowing motorists escape a conviction and penalty points.

* The failure, thus far, of an initiative to introduce another payment option for road traffic fines.

It is a specific offence not to produce a driving licence in court. However, in most cases the legislation, which was introduced by Mr Varadkar, is not being enforced.

Department of Justice figures confirmed that less than half of motorists appearing in court over a four-month period last year had brought their licence with them. Many avoided points as a result because their failure to produce their licence was not followed up on.

Mr Varadkar voiced his concerns about this phenomenon at a number of road safety working groups, which involve his department, the Department of Justice, the gardai and the Courts Service. However, he has not been satisfied by responses to his concerns, the Sunday Independent understands.

It is understood the Department of Justice is reluctant to intervene as it could be considered an encroachment on the independence of the judiciary. A further source of frustration for Mr Varadkar has been the delay in implementing what is known as the "third payment option".

This is an initiative which would give motorists three chances to pay a motoring fine – rather than the two that exist – before they would have to appear in court.

He has been trying to move on the issue for 18 months, but hasn't been able to make progress due to an apparent disagreement between the gardai and the Courts Service related to the IT system which would process the payments.

Mr Varadkar has also privately expressed concerns that the O'Mahony investigation into allegations gardai were abusing the penalty points system was not thorough.

The investigation did not find any evidence of corruption in the force in relation to the cancellation of penalty point notices, but recommended three officers be disciplined.